TW201730252A - Polyvinyl alcohol film for producing polarizing film, polarizing film and polarizing plate using polyvinyl alcohol film for producing polarizing film, and production method for polyvinyl alcohol film for producing polarizing film - Google Patents

Abstract

A polyvinyl alcohol film that is for producing a polarizing film, that is 5-60 [mu]m thick, that is 2 m wide or wider, and that is 2 km long or longer. The polyvinyl alcohol film is characterized in that, when the polyvinyl alcohol film is immersed in 30 DEG C water for 15 minutes, the width direction (TD direction) swelling degree X (%) and the length direction (MD direction) swelling degree Y (%) of the polyvinyl alcohol film satisfy conditions (1) and (2). (1) 110 ≤ Y ≤ 140 (2) 1.01 ≤ Y/X ≤ 1.2.

Description

Polyvinyl alcohol-based film for producing a polarizing film, polarizing film using the polyvinyl alcohol-based film, polarizing plate, and polyvinyl alcohol-based film for producing polarizing film

The present invention relates to a polyvinyl alcohol-based film for producing a polarizing film (hereinafter sometimes referred to as a "polyvinyl alcohol-based film"), and in particular, it is preferable to obtain excellent dyeability, high degree of polarization, and low color unevenness. A polyvinyl alcohol-based film of a polarizing film, a polarizing film using the polyvinyl alcohol-based film, a polarizing plate, and a method for producing a polyvinyl alcohol-based film for producing a polarizing film.

In the past, a polyvinyl alcohol-based film has been used as a film having excellent transparency and has been used in many applications, and one of its effective uses is a polarizing film. This polarizing film is used as a basic constituent element of a liquid crystal display, and in recent years, its use in equipment requiring high quality and high reliability is expanding.

In this case, as the screen of the liquid crystal television, the multi-functional portable terminal, and the like are increased in brightness, high in definition, large in area, and thinned, a polarizing film having excellent polarizing performance is required. Specifically, the degree of polarization is improved and the color unevenness is solved.

In general, a polyvinyl alcohol-based film for producing a polarizing film is produced from an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method. Specifically, an aqueous solution of a polyvinyl alcohol-based resin is cast on a casting mold such as a casting drum or an endless belt to form a film, and after the film obtained by forming the film is peeled off from the casting mold, the nip roll is used. It is conveyed in the traveling direction (MD direction), and is dried by using a hot roll or a floating dryer. In this conveyance step, since the film obtained by film formation is stretched in the traveling direction (MD direction), the polyvinyl alcohol-based polymer is likely to be aligned in the MD direction.

On the other hand, in general, a polarizing film is produced by swelling a polyvinyl alcohol-based film, which is a raw material roll, in water (including warm water), followed by dyeing and stretching with a dichroic dye such as iodine. In the swelling step, the polyvinyl alcohol-based film must be swollen rapidly in the thickness direction. Further, it is necessary to uniformly swell it in the dyeing step so that the dye is smoothly immersed in the inside of the film. Further, the extending step is a step of stretching the dyed film in the traveling direction (MD direction) to highly align the dichroic dye in the film, and in order to improve the polarizing property of the polarizing film, the polyvinyl alcohol becomes a raw material roll. The mesent must have good extensibility in the MD direction.

Further, in the production of the polarizing film, there are cases in which the order of the above-described stretching step and dyeing step is reversed. In other words, a case where the polyvinyl alcohol-based film, which is a raw material roll, is swollen in water (including warm water), and is stretched and dyed with a dichroic dye such as iodine, but in this case, in order to enhance the polarizing film The polarizing property, the polyvinyl alcohol film still has good swellability in the thickness direction and good elongation in the MD direction.

Further, in recent years, the polyvinyl alcohol film has been thinned due to the reduction in thickness of the polarizing film. This thin film has a problem of productivity such as breakage due to elongation at the time of manufacturing a polarizing film.

As a method of improving the swellability, for example, a method in which a polyol is added as a water swelling aid to a polyvinyl alcohol-based resin has been proposed (for example, see Patent Document 1). As a method for improving the elongation, for example, a method of specifying a ratio of a speed of a casting drum at the time of film formation to a final film winding speed (for example, see Patent Document 2), and a film after casting a film by a casting drum has been proposed. A method of drying by suspension (for example, refer to Patent Document 3), and a method of controlling the stretching state of a film obtained by film formation in a drying step (for example, see Patent Document 4). [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Laid-Open Patent Publication No. 2001-315141 (Patent Document 3) Japanese Laid-Open Patent Publication No. 2001-315142 (Patent Document 4) JP-A-2002-79531 Bulletin

[Problems to be Solved by the Invention] However, even if the method of the above patent document is provided, improvement in swelling property and elongation at the time of production of a polarizing film is not sufficient.

In the technique disclosed in the above-mentioned Patent Document 1, even if the swelling property of the entire polyvinyl alcohol-based film can be improved, the alignment state of the polyvinyl alcohol-based polymer is not considered, and the direction of travel in the production of the polarizing film is efficiently improved. The extensibility of (MD direction) is difficult. Conversely, the alignment state of the polymer is disturbed by the addition of the water swelling agent, and the uniform extension in the traveling direction (MD direction) tends to be difficult.

In the above-mentioned Patent Document 2, the extent of stretching in the MD direction (stretching condition) when the polyvinyl alcohol-based film is produced is specified. However, if the stretching in the TD direction is not considered, the improvement in the elongation at the time of producing the polarizing film is not sufficient. In general, in the production of a polarizing film, it is difficult to extend the polyvinyl alcohol-based film that has been aligned in the MD direction in the MD direction. In other words, it is difficult to forcibly stretch the molecular chain by stretching the polyvinyl alcohol-based polymer that has been aligned in the MD direction in the MD direction. On the contrary, it is relatively easy to stretch the polyvinyl alcohol-based polymer which has been aligned in the TD direction in the MD direction. However, if the alignment of the polymer in the TD direction is not uniform, the polarizing film cannot be uniformly stretched in the MD direction during the production of the polarizing film. Patent Document 2 discloses an example in which the polyvinyl alcohol-based film is not stretched in the MD direction (an example of unstretching), but only the above-mentioned shrinkage stress depending on Poisson's ratio. There is a problem that the polymer alignment in the TD direction cannot be sufficiently uniformized due to the shrinkage stress due to dehydration. In other words, if the width direction is not extended in the TD direction or the width direction is not fixed at least, the uniform alignment state of the polymer in the TD direction cannot be obtained, and the elongation in the MD direction during the manufacture of the improved polarizing film is insufficient. Further, there is no description about the orientation in the thickness direction, and it is not possible to control the swellability at the time of production of the polarizing film.

In the technique disclosed in the above Patent Document 3, the film after the film formation can be uniformly dried, but the alignment of the polymer cannot be controlled, and the improvement in the swelling property and the elongation at the time of producing the polarizing film is not sufficient. In the technique disclosed in the above Patent Document 4, the film thickness of the polyvinyl alcohol-based film can be uniformly formed, but the alignment of the polymer cannot be controlled, and the improvement in the swelling property and the elongation property in the production of the polarizing film is not improved. enough.

Thus, the present invention provides a polyvinyl alcohol for producing a polarizing film which is excellent in swellability and elongation at the time of production of a polarizing film, and which has a high polarizing property and a small color unevenness. The film, in particular, provides a polyvinyl alcohol-based film for producing a polarizing film which does not break during the production of the thin polarizing film, and further comprises: a polyvinyl alcohol-based film for producing a polarizing film. A method of producing a polarizing film, a polarizing plate, and a polyvinyl alcohol-based film for producing a polarizing film. [Means for solving the problem]

The inventors of the present invention have intensively studied in view of the circumstances, and found that the ratio of the swelling degree X (%) in the width direction (TD direction) to the swelling degree Y (%) in the traveling direction (MD direction) is within a specific range. The polyvinyl alcohol-based film is excellent in swellability and stretchability at the time of production of a polarizing film, and the polarizing film obtained using the polyvinyl alcohol-based film has high polarizing performance and is small in color unevenness.

That is, the first aspect of the present invention is a polyvinyl alcohol-based film for producing a polarizing film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, characterized in that the polyvinyl alcohol-based film is 30. When immersed in water at °C for 15 minutes, the swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the longitudinal direction (MD direction) satisfy the following conditions (1) and (2): 1) 110≦Y≦140; (2)1.01≦Y/X≦1.2.

In particular, when the polyvinyl alcohol-based film is immersed in water at 30 ° C for 15 minutes, the swelling degree Z (%) in the thickness direction satisfies the polyvinyl alcohol-based film for producing a polarizing film under the following condition (3). The second gist of the present invention: (3) 140 ≦ Z ≦ 170.

Further, the characteristic is the offset ΔX (%) of the swelling degree X (%) in the width direction (TD direction), the ΔY (%) of the swelling degree Y (%) in the longitudinal direction (MD direction), and the thickness direction. The polyvinyl alcohol-based film for producing a polarizing film, which is within 5% of the offset ΔZ (%) of the degree of swelling Z (%), is the third gist of the present invention.

Further, a polyvinyl alcohol-based film for producing a polarizing film which satisfies the following conditions (4) and (5) is the fourth gist of the present invention: (4) In-plane retardation Rxy (nm): 100~ 200 nm; (5) The alignment axis, that is, the intersection angle θ (°) of the retardation axis and the width direction, that is, the TD direction is 20° or less; wherein the in-plane phase difference Rxy (nm) is in the polyvinyl alcohol film. The refractive index in the width direction (TD direction) is nx, the refractive index in the longitudinal direction (MD direction) is ny, and the thickness is d (nm), and the value calculated by the following formula (A): (A) Rxy (nm) )=|nx-ny|×d(nm).

In particular, a polyvinyl alcohol-based film for producing a polarizing film having an offset ΔRxy (nm) in which the in-plane retardation Rxy (nm) in the width direction (TD direction) is 10 nm or less is the fifth aspect of the present invention.

Among them, a polyvinyl alcohol-based film for producing a polarizing film having an offset Δθ (°) of a crossing angle θ (°) of 10 or less is the sixth gist of the present invention.

Further, a polyvinyl alcohol-based film for producing a polarizing film having a thickness of 5 to 30 μm is the seventh gist of the present invention.

Further, the present invention relates to a polarizing film characterized in that the polyvinyl alcohol-based film for producing a polarizing film is used as the eighth gist.

Moreover, the present invention provides a polarizing plate characterized by comprising the polarizing film and a protective film provided on at least one surface of the polarizing film as a ninth aspect.

Further, the present invention relates to a method for producing a polyvinyl alcohol-based film for producing a polarizing film, which is obtained by a continuous casting method using an aqueous solution of a polyvinyl alcohol-based resin, and after being peeled off from a casting mold, in a traveling direction In the (MD direction), the polyvinyl alcohol-based film is continuously dried and stretched in the width direction (TD direction) to obtain a polyvinyl alcohol-based film, which is characterized in that the polyvinyl alcohol-based film is immersed in water at 30 ° C for 15 minutes. The swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction) satisfy the following conditions (1) and (2) as the tenth gist: (1) 110 ≦ Y ≦140; (2) 1.01≦Y/X≦1.2.

In particular, a method for producing a polyvinyl alcohol-based film for producing a polarizing film which is extended in the width direction (TD direction) by a stretching ratio of 1.05 to 1.5 times is the eleventh aspect of the present invention.

Further, a method for producing a polyvinyl alcohol-based film for producing a polarizing film which is extended in the width direction (TD direction) at 50 to 150 ° C is the twelfth aspect of the present invention.

In addition, a method for producing a polyvinyl alcohol-based film for producing a polarizing film having a water content of 0.5 to 15% by weight in the film before stretching in the width direction (TD direction) is the 13th aspect of the present invention.

In the case where the width direction (TD direction) is temporarily extended more than 1.3 times, and the stretching ratio in the final width direction (TD direction) is 1.05 to 1.5 times, the size is contracted to manufacture a polarizing film. The method for producing a polyvinyl alcohol film is the fifteenth aspect of the present invention.

In addition, a method for producing a polyvinyl alcohol-based film for producing a polarizing film having a dimensional change ratio of 0.8 to 1.0 in the traveling direction (MD direction) of the film before and after the extension in the width direction (TD direction) is used as the present invention. The 15th gist. [Effects of the Invention]

The polyvinyl alcohol-based film for producing a polarizing film of the present invention can provide excellent swellability and elongation at the time of production of a polarizing film, and does not break even when a thin polarizing film is produced, exhibits high polarizing performance and has less color unevenness. Polarized film. Further, the present invention is based on the technical idea of improving the swellability and extensibility at the time of production of a polarizing film by improving the swelling property of the polyvinyl alcohol-based film in the traveling direction (MD direction).

The present invention will be described in detail below. The polyvinyl alcohol-based film for producing a polarizing film of the present invention has a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and has the following characteristics. Specifically, the aqueous solution of the polyvinyl alcohol-based resin is formed into a film by a continuous casting method, and after the film obtained by the film formation is peeled off from the casting mold, it is continuously conveyed in the traveling direction (MD direction). Drying and stretching in the width direction (TD direction) are obtained.

When the polyvinyl alcohol-based film produced by the above method is immersed in water at 30 ° C for 15 minutes, the swelling degree X (%) in the width direction (TD direction) and the swelling degree in the traveling direction (MD direction) Y (%) satisfies the physical property values of both of the following conditions (1) and (2). This is a feature of the invention. Even if only one physical property value is satisfied, the object of the present invention cannot be achieved. (1) 110≦Y≦140; (2)1.01≦Y/X≦1.2.

The above conditions (1) and (2) can be achieved, for example, by extending the width direction (TD direction) of the film obtained by film formation. In this case, the stretching ratio is preferably 1.05 to 1.5 times, and is 1.1 to 1.45 times. Very good, 1.2 to 1.4 times better. The stretching ratio in the width direction (TD direction) is too low or too high, and there are control and phase difference between the swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction). The control tends to be difficult, and the swelling property and the elongation property at the time of production of the polarizing film tend to be lowered.

The condition (1) specifies the degree of swelling Y (%) in the traveling direction (MD direction), which is within the range of the known technique. The degree of swelling Y (%) must be 110% or more and 140% or less, preferably 115% or more and 135% or less, and more preferably 120% or more and 130% or less. When the degree of swelling Y (%) is less than the lower limit, the elongation at the time of production of the polarizing film is lowered, which is less desirable. Conversely, if the degree of swelling exceeds the upper limit, the degree of polarization of the polarizing film is lowered, which is less preferable.

The condition (2) specifies the ratio (Y/X) of the swelling degree Y (%) in the traveling direction (MD direction) to the swelling degree X (%) in the width direction (TD direction). The most characteristic feature of the present invention is that the degree of swelling Y (%) in the traveling direction (MD direction) is larger than the swelling degree X (%) in the width direction (TD direction) in a specific range. In the conventional polyvinyl alcohol-based film, the ratio is usually 1 or less. This is because the molecular chain of the polyvinyl alcohol-based polymer is usually oriented in the traveling direction (MD direction) and is not easily swollen in this direction.

The ratio (Y/X) of the swelling degree Y (%) in the traveling direction (MD direction) to the swelling degree X (%) in the width direction (TD direction) must satisfy the condition (2) 1.01 ≦ Y / X ≦ 1.2, preferably The following condition (2') is satisfied, and the following condition (2'') is particularly preferable: (2') 1.03 ≦ Y / X ≦ 1.15; (2'') 1.05 ≦ Y / X ≦ 1.1. When the Y/X is less than the lower limit, the elongation at the time of production of the polarizing film is insufficient, which is less desirable. Conversely, when the value exceeds the upper limit, the degree of polarization of the polarizing film is lowered, which is less preferable.

In addition, when the polyvinyl alcohol-based film of the present invention is immersed in water at 30 ° C for 15 minutes, the degree of swelling Z (%) in the thickness direction preferably satisfies the following condition (3), and the following condition (3') is particularly preferable. It is better to satisfy the following conditions (3''): (3) 140≦Z≦170 (3')143≦Z≦169 (3'')145≦Z≦168

The degree of swelling Z (%) in the present invention is the degree of swelling X (%) in the width direction (TD direction), the degree of swelling Y (%) in the direction of travel (MD direction), and the weight after impregnation of the film and the impregnated The weight of the film after drying, and the value calculated according to the following formula. Swelling degree Z (%) = 1000000 × weight after immersion (g) / weight after drying (g) / X / Y

When the degree of swelling Z (%) is too low, the swelling property at the time of production of the polarizing film tends to decrease. Conversely, if the degree of swelling is too high, the degree of polarization of the polarizing film tends to decrease. The degree of swelling Z (%) is clearly known from the conditions (1), (2), and (3), and the swelling degree in the width direction (TD direction) and the swelling direction in the traveling direction (MD direction) are large. This is because the molecular chain of the polyvinyl alcohol-based polymer is a chemical structure mainly oriented in the plane direction and easily swollen in the thickness direction. Due to this chemical structure, the polyvinyl alcohol-based film can be swollen quickly and uniformly during the swelling step in the production of the polarizing film.

Further, the offset ΔX (%) of the swelling degree X (%) in the width direction (TD direction) of the polyvinyl alcohol-based film of the present invention, and the offset ΔY of the swelling degree Y (%) in the traveling direction (MD direction) ( The offset ΔZ (%) of the swelling degree Z (%) in the thickness direction is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less. If the offset is too large, the polarizing film tends to have color unevenness.

Further, in the present invention, as a method for satisfying the conditions (1), (2), and (3), a film obtained by peeling off a casting mold according to the present invention may be carried out in the width direction (TD direction). In addition to the method of stretching, a method of adjusting the drying conditions of the polyvinyl alcohol-based resin aqueous solution, a method of adjusting the chemical structure of the polyvinyl alcohol-based resin, and the like may be mentioned.

Further, the polyvinyl alcohol-based film produced by the above method preferably satisfies the physical property values of the following conditions (4) and (5): (4) in-plane retardation Rxy (nm): 100 to 200 nm; 5) The intersection angle θ (°) of the alignment axis (late phase axis) and the width direction (TD direction) is 20° or less. Here, the in-plane retardation Rxy (nm) is such that the refractive index in the width direction (TD direction) is nx in the polyvinyl alcohol-based film, the refractive index in the traveling direction (MD direction) is ny, and the thickness is d (nm). The value calculated by the following formula (A): (A) Rxy (nm) = | nx - ny | × d (nm).

The in-plane retardation Rxy (nm) is particularly preferably 110 to 180 nm, and more preferably 130 to 170 nm. When the in-plane retardation Rxy (nm) is too small, the elongation in the MD direction tends to decrease during the production of the polarizing film. If the in-plane retardation film is too large, the polarizing film tends to have color unevenness.

The offset ΔRxy (nm) of the in-plane retardation Rxy (nm) in the width direction (TD direction) is preferably 10 nm or less, more preferably 5 nm or less, and still more preferably 3 nm or less. When the offset ΔRxy is too large, the polarizing film tends to be uneven in color.

The intersection angle θ (°) of the alignment axis (late phase axis) and the width direction (TD direction) is preferably 20° or less, more preferably 10° or less, and even more preferably 5° or less. When the crossing angle θ (°) is too large, the elongation in the MD direction tends to decrease during the production of the polarizing film.

The deviation Δθ (°) of the intersection angle θ (°) in the width direction (TD direction) is preferably 10° or less, more preferably 5° or less, and even more preferably 3° or less. When the offset Δθ (°) is too large, the polarizing film tends to be uneven in color.

In addition, as a method of controlling the in-plane retardation Rxy (nm) and the crossing angle θ (°), in addition to the method of extending the film obtained by peeling the casting mold in the width direction (TD direction) of the present invention, Further, a method of adjusting the drying conditions of the aqueous solution, a method of adjusting the chemical structure of the polyvinyl alcohol-based resin, and the like may be mentioned.

Here, a method for producing a polyvinyl alcohol-based film for producing a polarizing film of the present invention will be described in more detail in the order of steps.

[Film material] First, the polyvinyl alcohol resin and the aqueous solution used in the present invention will be described. In the present invention, as the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film, an unmodified polyvinyl alcohol-based resin, that is, a polyvinyl acetate obtained by polymerizing vinyl acetate, is used for saponification. The resulting resin. A resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) copolymerizable with vinyl acetate may be used as needed. Examples of the component copolymerizable with vinyl acetate include an unsaturated carboxylic acid (including, for example, a salt, an ester, a guanamine, a nitrile, etc.); and an olefin having 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene). , isobutylene, etc.); vinyl ethers; unsaturated sulfonates. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying a hydroxyl group after saponification may also be used. These may be used alone or in combination of two or more.

Further, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in its side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can be obtained by, for example, (i) vinyl acetate and 3,4-diethyloxy-1-butene. a method of saponification of a copolymer; (ii) a method of saponifying and decarboxylating a copolymer of vinyl acetate and ethylene vinyl carbonate; (iii) a vinyl acetate with 2,2-dialkyl-4-ethylene A method of saponification and deketalization of a copolymer of 1,3-dioxolane; (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably from 100,000 to 300,000, preferably from 110,000 to 280,000, and more preferably from 120,000 to 260,000. When the weight average molecular weight is too small, when the polyvinyl alcohol-based resin is used as an optical film, sufficient optical performance tends to be difficult to obtain. When the polarizing film is formed by using a polyvinyl alcohol-based film, stretching may become difficult. The tendency. Further, the weight average molecular weight of the polyvinyl alcohol-based resin is measured by a GPC-MALS method.

The average saponification degree of the polyvinyl alcohol-based resin used in the present invention is usually preferably 98 mol% or more, more preferably 99 mol% or more, more preferably 99.5 mol% or more, and even more preferably 99.8 mol% or more. . When the average degree of saponification is too small, when a polyvinyl alcohol-based film is used as a polarizing film, sufficient optical performance may not be obtained. Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

The polyvinyl alcohol-based resin used in the present invention may be used in combination of two or more kinds of modified species, a modification amount, a weight average molecular weight, and an average degree of saponification.

In addition to the polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin aqueous solution contains glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, or trihydroxyl, if necessary. When a plasticizer such as methyl propane or a non-ionic, anionic or cationic surfactant is used, it is preferable from the viewpoint of film formability. These may be used alone or in combination of two or more.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in this manner is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, more preferably 20 to 50% by weight. When the resin concentration of the aqueous solution is too low, the drying load is increased, and the productivity tends to be lowered. When the viscosity is too high, the viscosity is too high, and the uniform dissolution tends to be difficult.

Then, the obtained polyvinyl alcohol-based resin aqueous solution was subjected to defoaming treatment. Examples of the defoaming method include a method of static defoaming, and defoaming by a multiaxial extruder. As the multi-axis extruder, if it is a multi-axis extruder having a vent hole, a twin-screw extruder having a vent hole is usually used.

[Film Forming Step] After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution was introduced into the T-slot mold in a predetermined amount, and discharged and cast on a rotating casting drum, and film formation was carried out by a continuous casting method.

The continuous casting method in the present invention refers to, for example, a method in which an aqueous solution of a polyvinyl alcohol-based resin is discharged from a T-slot and cast into a casting mold such as a rotating casting drum, an endless belt, or a resin film to form a film. The film obtained by the film formation is peeled off from the casting mold, and then conveyed in the traveling direction (MD direction), and continuously dried by a hot roll. For example, the film may be heat-treated by a floating dryer.

The resin temperature of the polyvinyl alcohol-based resin aqueous solution at the outlet of the T-slot is preferably from 80 to 100 ° C, preferably from 85 to 98 ° C. When the resin temperature of the polyvinyl alcohol-based resin aqueous solution is too low, the flow tends to be poor, and if it is too high, foaming tends to occur.

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa·s at the time of discharge, and is particularly preferably 70 to 150 Pa·s. If the viscosity of the aqueous solution is too low, the flow tends to be poor, and if it is too high, casting tends to be difficult.

The discharge rate of the polyvinyl alcohol-based resin aqueous solution discharged from the T-slot to the casting drum is preferably 0.2 to 5 m/min, more preferably 0.4 to 4 m/min, and even more preferably 0.6 to 3 m/min. If the discharge speed is too slow, the productivity tends to be lowered, and if it is too fast, casting tends to be difficult.

The diameter of the casting drum is preferably 2 to 5 m, preferably 2.4 to 4.5 m, and more preferably 2.8 to 4 m. If the diameter is too small, the drying zone on the casting drum tends to be short, and the speed tends to be difficult to increase. If the diameter is too large, the conveyability may be lowered.

The width of the casting drum is preferably 4 m or more, particularly preferably 4.5 m or more, more preferably 5 m or more, and particularly preferably 5 to 6 m. If the width of the casting drum is too small, the productivity tends to be lowered.

The casting drum preferably has a rotation speed of 3 to 50 m/min, preferably 4 to 40 m/min, and more preferably 5 to 35 m/min. If the rotation speed is too slow, the productivity tends to be lowered, and if it is too fast, the drying tends to be insufficient.

The surface temperature of the casting drum is preferably 40 to 99 ° C, preferably 60 to 95 ° C. If the surface temperature is too low, drying tends to be poor, and if it is too high, foaming tends to occur.

[Film formed by film formation] The film obtained by film formation as described above [film before stretching in the width direction (TD direction)] preferably has a water content of 0.5 to 15% by weight, and is 1 to 13% by weight. Good, 2~12% by weight is even better. Regardless of whether the water content is too low or too high, there is a tendency for the target polymer to be aligned, that is, the purpose of exhibiting the degree of swelling and elongation is difficult.

In order to adjust the water content, when the moisture content of the film before stretching in the width direction (TD direction) is too high, it is preferred to dry the film before extending in the width direction (TD direction), and conversely, in the width direction (TD) When the moisture content of the film before the stretching is too low, it is preferred to perform humidity conditioning before extending in the width direction (TD direction). It is more preferable to adjust the conditions of the drying step in such a manner that the water content is in the above range.

The drying can be carried out by a known method using a heating roll, an infrared heater or the like. In the present invention, it is preferable to use a plurality of heating rolls, and the temperature of the heating roll is preferably 40 to 150 ° C, more preferably 50 to 120 ° C. . Further, in order to adjust the water content, the humidity control zone may be provided before the extension in the width direction (TD direction).

[Transportation and Extension Step] Then, the film obtained by the above-described method and having the moisture content adjusted is conveyed in the traveling direction (MD direction), and continuously or intermittently performed in the width direction (TD direction). extend.

In the present invention, it is sufficient that the film obtained by film formation is not particularly required to be stretched in the traveling direction (MD direction) and conveyed at a tensile tension to the extent that the film is not bent. As a matter of course, due to the extension in the width direction (TD direction), necking depending on the Poisson's ratio occurs in the traveling direction (MD direction), and dehydration shrinkage occurs in the traveling direction (MD direction) during drying. The film will shrink in size in the direction of travel (MD direction).

Even, it is not preferable to extend in the traveling direction (MD direction) to the extent that the dimension of the traveling direction (MD direction) is stretched. Before and after the extension of the width direction (TD direction), the dimensional change rate of the traveling direction (MD direction) is preferably 0.8 to 1.0, preferably 0.9 to 1.0, more preferably 0.95 to 1.0. If the dimensional change rate is too small or too large, the shift of the swelling degree tends to increase, and there is a tendency that the target polymer is aligned, that is, the target swelling degree tends to be difficult.

The conveying speed of the film obtained by the film formation in the traveling direction (MD direction) is preferably 5 to 30 m/min, more preferably 7 to 25 m/min, and even more preferably 8 to 20 m/min. If the conveyance speed is too slow, the productivity tends to be lowered. If the conveyance speed is too fast, the color unevenness of the polarizing film tends to increase.

At the same time, the method of carrying the film formed in the film in the traveling direction (MD direction) and the film in the width direction (TD direction) is not particularly limited. For example, the both ends of the film in the width direction are held by a plurality of jigs. It is ideal to carry out handling and extension at the same time. In this case, the arrangement of the jigs at the respective end portions is preferably 200 mm or less, the pitch is preferably 100 mm or less, and the pitch is 50 mm or less. When the distance between the jigs is too wide, the film after stretching may be bent, or the thickness of both ends of the obtained polyvinyl alcohol-based film in the width direction may be uneven, and the phase difference may become uneven. Further, it is preferable that the gripping position of the jig (the tip end portion of the jig) is 100 mm or less from both ends in the width direction of the film formed by the film formation. When the holding position (front end portion) of the jig is too large at the center portion in the film width direction, the end portion of the film to be discarded tends to increase and the product width tends to be narrow.

The polyvinyl alcohol-based film specified in the present invention can be obtained by extending the width direction (TD direction) of the film obtained by film formation as described above, and the stretching ratio at this time is preferably 1.05 to 1.5 times. It is 1.1~1.45 times better, 1.15~1.4 times better, and 1.2~1.3 times better. Even if the stretching ratio in the width direction (TD direction) is too low or too high, the swelling property and the stretchability at the time of production of the polarizing film tend to be lowered.

The step of extending the continuity in the width direction (TD direction) may be one stage (one time) or multiple stages (multiple times) such that the total stretching ratio becomes the range of the above stretching ratio (also referred to as successive stretching). For example, after the extension of the first stage, the simple conveyance in which the width direction (TD direction) is fixed may be performed, and the extension after the second stage may be performed. In particular, in the case of a thin film, by inserting this simple conveyance step, the stress of the film can be relaxed to avoid breakage. When the insertion step of the fixed width is inserted, the fixed width can also be set to be narrower than the width after the extension of the first stage. The film that has just been stretched easily shrinks due to stress relaxation, and shrinkage due to dehydration also occurs, so that the fixed width can be set to be narrower than the contraction width. However, if it is narrower than the shrinkage width, it is less desirable because the film is bent. This extension step is preferably carried out after the drying step of the film, but may be carried out separately at least one time before the drying step of the film and after the drying step, or may be carried out in the drying step.

In a preferred embodiment of the present invention, the film may be temporarily extended more than 1.3 times in the width direction (TD direction), and then the stretching ratio in the final width direction (TD direction) may be 1.05 to 1.5 times. The method of shrinking the size. In this case, after temporarily extending more than 1.3 times, the film may be simply conveyed at a fixed width of 1.05 to 1.5 times the stretching ratio. With this method, the stress of the film can be relaxed, especially in the case of a thin film.

In the present invention, the film obtained by film formation preferably extends in the width direction (TD direction) at 50 to 150 ° C, preferably 60 to 140 ° C, more preferably 70 to 130 ° C. Even if the stretching temperature is too low or too high, the elongation at the time of production of the polarizing film tends to decrease. When the stretching is performed successively or intermittently, the extension temperature may be changed at each extension stage, or the temperature gradient may be set during the extension.

In the present invention, the extension time for the film obtained by film formation in the width direction (TD direction) is preferably 2 to 60 seconds, preferably 5 to 45 seconds, and 10 to 30 seconds. good. If the stretching time is too short, the film tends to be broken. On the contrary, if the stretching time is too long, the equipment load tends to increase. When the successive extension is performed, the extension time can also be changed at each extension stage.

In the present invention, after the film obtained by the film formation is stretched in the width direction (TD direction), the heat treatment may be performed by a floating dryer or the like. The heat treatment temperature is preferably 60 to 200 ° C, preferably 70 to 150 ° C, and more preferably 100 to 140 ° C. When the heat treatment temperature is too low, the dimensional stability tends to be lowered. On the contrary, if the heat treatment temperature is too high, the elongation at the time of production of the polarizing film tends to be lowered. Moreover, the heat treatment time should be 1 to 60 seconds, which is particularly good for 5 to 30 seconds. When the heat treatment time is too short, the dimensional stability tends to be lowered. Conversely, when the heat treatment time is too long, the swelling property and the elongation property at the time of production of the polarizing film tend to be lowered.

[Polyvinyl alcohol-based film for producing a polarizing film] The polyvinyl alcohol-based film for producing a polarizing film of the present invention is obtained in this manner, and finally wound around a roll to form a product. The thickness of the polyvinyl alcohol-based film is preferably from 5 to 60 μm in view of the in-plane retardation, and is particularly preferably from 5 to 45 μm in terms of thickness reduction of the polarizing film, and more preferably from 5 to 30 μm. 10~20μm is especially good. The thickness of the polyvinyl alcohol-based film is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the discharge amount (discharge rate) to the casting mold, the stretching ratio, and the like.

The width of the polyvinyl alcohol-based film is preferably 2 m or more, and is preferably 3 m or more from the viewpoint of increasing the area, and is more preferably 4 to 6 m from the viewpoint of avoiding breakage.

The length of the polyvinyl alcohol-based film is preferably 2 km or more, and is preferably 3 km or more in terms of a large area, and more preferably 3 to 50 km from the viewpoint of transporting weight.

The polyvinyl alcohol-based film for producing a polarizing film of the present invention is very effective as a raw material roll film of a polarizing film. Hereinafter, a polarizing film composed of the polyvinyl alcohol-based film and a method for producing a polarizing plate will be described.

[Manufacturing Method of Polarizing Film] The polarizing film of the present invention is produced by transferring the polyvinyl alcohol-based film from the roll and then transferring it horizontally, and swelling, dyeing, boric acid crosslinking, stretching, washing, drying, and the like.

The swelling step is carried out prior to the dyeing step. In addition to the staining on the surface of the polyvinyl alcohol-based film, the swelling step can prevent the dyeing unevenness and the like by swelling the polyvinyl alcohol-based film. Water is usually used as the treatment liquid in the swelling step. When the main component of the treatment liquid is water, an additive such as an iodinated compound or a surfactant, or an alcohol may be added in a small amount. The temperature of the swelling bath is usually about 10 to 45 ° C, and the time of immersion in the swelling bath is usually about 0.1 to 10 minutes.

In the swelling step, the degree of swelling of the polyvinyl alcohol-based film of the present invention is as described above, and when the degree of swelling of the film is measured after immersing in water at 30 ° C for 15 minutes, the degree of swelling in the width direction (TD direction) X ( %) The degree of swelling Y (%) with the traveling direction (MD direction) satisfies the physical property values of the following conditions (1) and (2): (1) 110 ≦ Y ≦ 140; (2) 1.01 ≦ Y / X≦1.2.

Further, as described above, the degree of swelling Z (%) in the thickness direction satisfies the following condition (3): (3) 140 ≦ Z ≦ 170.

The dyeing step is carried out by contacting the film with a liquid containing iodine or a dichroic dye. An aqueous solution of iodine-potassium iodide is usually used, and the concentration of iodine is 0.1 to 2 g/L, and the concentration of potassium iodide is preferably 1 to 100 g/L. The dyeing time is about 30 to 500 seconds. The temperature of the treatment bath should be 5 to 50 °C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent.

The boric acid crosslinking step is carried out using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g/L. When potassium iodide is allowed to coexist in the solution, the viewpoint of stability of polarization performance is preferable. The temperature during the treatment is about 30 to 70 ° C, the treatment time is preferably about 0.1 to 20 minutes, and the extension operation can be carried out during the treatment as needed.

The extension step is to make the film 3 to 10 times in the uniaxial direction, and it is preferable to carry out the extension of 3.5 to 6 times. At this time, it is possible to perform a slight extension in the direction perpendicular to the extending direction (preventing the degree of shrinkage in the width direction or the extension thereof). The temperature at the time of extension should be 40 to 170 °C. Further, the stretching ratio may be set to be in the above range at the end, and the stretching operation may be performed not only once but also in the manufacturing step.

The washing step can be carried out, for example, by immersing the polyvinyl alcohol-based film in an aqueous iodide solution such as water or potassium iodide to remove precipitates generated on the surface of the film. The potassium iodide concentration when using the potassium iodide aqueous solution may be about 1 to 80 g/L. The temperature during the cleaning treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Further, the water washing and the washing with the potassium iodide aqueous solution may be carried out as appropriate.

The drying step is carried out, for example, by drying the film at 40 to 80 ° C for 1 to 10 minutes in the atmosphere.

Thus, a polarizing film can be obtained, and the polarizing film preferably has a degree of polarization of 99.5% or more, and is particularly preferably 99.8% or more. If the degree of polarization is too low, the contrast in the liquid crystal display tends to decrease. In addition, in general, the degree of polarization is a light transmittance (H ₁₁ ) measured at a wavelength λ in a state in which two polarizing films are stacked in such a manner that their alignment directions are the same direction, and two polarized films are used. The light transmittance (H ₁ ) measured at the wavelength λ in a state in which the films are superposed in such a manner that the alignment directions are perpendicular to each other is calculated by the following equation. Polarization = [(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

Further, the polarizing film of the present invention preferably has a monomer permeability of 44% or more. When the monomer transmittance is too low, the brightness of the liquid crystal display tends to be insufficient. The monomer transmittance is a value obtained by measuring the light transmittance of the polarizing film monomer using a spectrophotometer.

Next, a method of producing the polarizing plate of the present invention using the polarizing film of the present invention will be described. The polarizing film of the present invention is suitable for producing a polarizing plate having less color unevenness and excellent polarizing performance.

[Manufacturing Method of Polarizing Plate] The polarizing plate of the present invention is produced by adhering the adhesive to the optically isotropic resin film of the protective film on one surface or both surfaces of the polarizing film of the present invention. Examples of the protective film include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cyclic olefin copolymer, polystyrene, polyether oxime, A film or sheet of a poly(aryl) ester, poly(4-methylpentene), poly(phenylene ether) or the like.

The bonding method is carried out by a known method. For example, by uniformly applying a liquid adhesive composition to a polarizing film, a protective film, or both, the two are attached together for pressure bonding and heating. Or by irradiation with active energy rays.

In addition, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied to one surface or both surfaces of the polarizing film, and the cured layer may be cured to form a polarizing plate. In this manner, the hardened layer can be replaced by the protective film to achieve film formation.

The polarizing film and the polarizing plate of the polyvinyl alcohol film of the invention have excellent polarizing performance, and are suitable for use in a portable information terminal, a personal computer, a television, a projector, a signboard, a desktop computer, and an electronic device. Liquid crystal display devices such as clocks, word processors, electronic papers, game machines, video recorders, cameras, photo albums, thermometers, stereos, automobiles, and mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, wearable displays Anti-reflection layer, optical communication equipment, medical equipment, building materials, toys, etc. for display elements (CRT, LCD, organic EL, electronic paper, etc.). [Examples]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. In addition, the "part" in the example means the weight basis.

Further, the properties of the polyvinyl alcohol-based film in the following examples and comparative examples (the degree of swelling, the degree of swelling, the in-plane retardation, the shift in the in-plane retardation, the alignment axis and the width direction) were carried out as follows. Measurement and evaluation of the characteristics of the polarizing film (polarization degree, monomer transmittance, and color unevenness). <Measurement conditions> [Swelling degree (%) of polyvinyl alcohol-based film] One film each having a width of 100 mm × a length of 100 mm was cut out from the center portion and the left and right end portions in the width direction of the obtained polyvinyl alcohol-based film, and It was immersed in water at 30 ° C for 15 minutes to swell. The swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction) were calculated from the dimensions before and after the immersion according to the following formula. The degree of swelling Z (%) in the thickness direction is one film each having a width of 100 mm × a length of 100 mm from the central portion and the left and right end portions in the width direction of the polyvinyl alcohol-based film, and immersed in water at 30 ° C for 15 minutes. After swelling, the film was taken out, and the film was unfolded on a filter paper (5A), and the filter paper (5A) was overlaid on the film, and 150 mm × 150 mm × 4 mm (4.4 × 10 ^-2 g / mm) was placed thereon. ² ) The SUS plate was removed for 5 seconds to remove the adhering water on the surface of the film. The film was quickly placed in a weighing bottle to measure the weight and set it as "weight after impregnation". The above operation was carried out in an environment of 23 ° C and 50% RH. Then, the film was placed in a dryer at 105 ° C for 16 hours to remove moisture from the film, and then the film was taken out, quickly placed in a weighing bottle to measure the weight, and it was designated as "weight after drying". Then, the degree of swelling Z (%) in the thickness direction is calculated according to the following formula. Swelling degree X (%) = 100 × width in the TD direction after immersion (mm) / width in the TD direction before immersion (mm) Swelling degree Y (%) = 100 × width in the MD direction after immersion (mm) / Width (mm) in the MD direction before immersion, degree of swelling Z (%) = 1000000 × weight after immersion (g) / weight after drying (g) / X / Y

[Offset of swelling degree (%)] The value of the swelling degree X (%) in the width direction (TD direction) obtained by the above measurement (three points at the center portion and the left and right end portions), and the maximum value and the minimum value are taken. The difference is determined as the offset ΔX (%) of the swelling degree in the width direction (TD direction). Similarly, the offset ΔY (%) of the swelling degree in the traveling direction (MD direction) and the offset ΔZ (%) of the swelling degree in the thickness direction were obtained.

[In-plane phase difference Rxy (nm), in-plane phase difference shift ΔRxy (nm), alignment axis (late phase axis) and width direction (TD direction) intersection angle θ (°) and intersection angle θ offset Δθ (°)] A test piece having a length of 4 cm × a width of 4 cm was cut out from the central portion in the width direction of the obtained polyvinyl alcohol-based film and the left and right end portions (inside of the film edge 10 cm), and a phase difference measuring device was used. "KOBRA-WR" manufactured by Oji Scientific Instruments Co., Ltd.) measures the in-plane phase difference Rxy (nm) and the intersection angle θ (°) between the alignment axis (late phase axis) and the width direction (TD direction). Further, among the in-plane phase differences Rxy (nm) between the center portion and the left and right end portions in the width direction obtained by the above measurement, the difference between the maximum value and the minimum value is defined as the offset of the in-plane phase difference ΔRxy (nm ). Further, among the intersection angles θ (°) between the central portion in the width direction and the left and right end portions obtained by the above measurement, the difference between the maximum value and the minimum value is defined as the deviation Δθ (°) of the intersection angle θ (°). ).

[Dimensional change rate] Before the extension in the width direction (TD direction), the distance (1 point) is marked by the distance of lm in the traveling direction (MD direction) by the singular pen. After extending in the width direction (TD direction), the distance L(m) between the two points is measured by a vernier caliper, and the dimensional change rate is calculated according to the following formula: Dimensional change rate = L (m) / l (m).

[Polarization degree (%), monomer transmittance (%)] A test piece having a length of 4 cm × a width of 4 cm was cut out from the center portion in the width direction of the obtained polarizing film, and an automatic polarizing film measuring device (manufactured by JASCO Corporation) was used: VAP7070) measures the degree of polarization (%) and monomer penetration (%).

[Color unevenness] A test piece having a length of 30 cm × a width of 30 cm was cut out from the central portion in the width direction of the obtained polarizing film, and two polarizing plates held in an orthogonally polarized state at an angle of 45° (monomer transmittance 43.5) After the difference between % and the degree of polarization of 99.9%, a light box having a surface illuminance of 14,000 lx was used, and the optical color unevenness was observed in a penetration mode, and evaluated by the following criteria. (Evaluation criteria) ○...No color unevenness △...Inconsistent color unevenness ×...Color unevenness

<Example 1> (Production of polyvinyl alcohol-based film) 1,000 kg of a polyvinyl alcohol-based resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer, and an interface 0.25 kg of polyoxyethylene laurylamine as an active agent was placed in a 5,000 L dissolution tank, and the mixture was heated to 150 ° C in a stirred state to carry out pressure dissolution, and a polyvinyl alcohol-based resin having a resin concentration of 25% by weight was obtained by concentration adjustment. Aqueous solution. Then, the polyvinyl alcohol-based resin aqueous solution was supplied to a twin-screw extruder to perform defoaming, and then the temperature of the aqueous solution was set to 95 ° C, and it was discharged from the T-slot discharge port (discharge rate: 2.5 m/min) and cast in a rotation. The casting drum is used to make the film. The film obtained by the film formation was peeled off from the casting drum, and conveyed in the traveling direction (MD direction), and the surface of the film and the back surface were alternately brought into contact with a total of 10 heating rolls to perform drying. Thereby, a film (width 2 m, thickness 60 μm) having a water content of 10% by weight was obtained. Then, the left and right end portions of the film were held at a jig pitch of 45 mm, and the film was conveyed at a speed of 8 m/min in the traveling direction (MD direction), and 1.2 in the width direction (TD direction) at 120 ° C using an extension machine. Double extension. Before and after the extension in the width direction (TD direction), the dimensional change rate in the traveling direction (MD direction) was 0.96. Finally, heat treatment was performed at 120 ° C for 10 seconds to obtain a polyvinyl alcohol-based film (having a width of 2.4 m, a thickness of 50 μm, and a length of 2 km). The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

(Preparation of Polarizing Film and Polarizing Plate) The obtained polyvinyl alcohol-based film was immersed in a water bath at a water temperature of 30 ° C in a state where it was taken out from a roll and conveyed in a horizontal direction, and was swollen in the traveling direction (MD). Direction) 1.7 times extension. Then, it was immersed in an aqueous solution of 30° C. consisting of 0.5 g/L of iodine and 30 g/L of potassium iodide, and was stretched 1.6 times in the traveling direction (MD direction), and then immersed in a composition of boric acid 40 g/L. In the aqueous solution (50 ° C) of potassium iodide 30 g/L, cross-linking of boric acid was carried out, and 2.1 times uniaxial stretching was performed in the traveling direction (MD direction). Finally, the mixture was washed with an aqueous solution of potassium iodide, and dried at 50 ° C for 2 minutes to obtain a polarizing film having a total stretching ratio of 5.8 times. No breakage occurred in this production. The characteristics of the obtained polarizing film are shown in Table 2. To the both surfaces of the polarizing film obtained above, a triethyl fluorene cellulose film having a film thickness of 40 μm was bonded using an aqueous polyvinyl alcohol solution as an adhesive, and dried at 70 ° C to obtain a polarizing plate.

<Example 2> In Example 1, the film obtained by film formation was extended by 1.4 times in the width direction (TD direction) at 120 ° C using a stretcher, and the fixed width was 2.4 m (equivalent to 1.2 times extension). A polyvinyl alcohol-based film (having a width of 2.4 m, a thickness of 50 μm, and a length of 2 km) was obtained in the same manner as in Example 1 except that the conveyance was carried out. Before and after the extension in the width direction (TD direction), the dimensional change rate in the traveling direction (MD direction) was 0.96. The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. No breakage occurred in this manufacturing. The characteristics of the obtained polarizing film are shown in Table 2.

<Example 3> In Example 1, the discharge rate at the time of film formation was set to 0.8 m/min, and the film (width: 2 m, thickness: 20 μm) having a water content of 5% by weight was subjected to 1.4 in the width direction (TD direction). A polyvinyl alcohol-based film (having a width of 2.6 m, a thickness of 15 μm, and a length of 2 km) was obtained in the same manner as in Example 1 except that the film was transported at a fixed width of 2.6 m (equivalent to a 1.3-fold extension). Before and after the extension in the width direction (TD direction), the dimensional change rate in the traveling direction (MD direction) was 0.98. The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. Although the polyvinyl alcohol-based film of the raw material roll was thin, the elongation step at the time of production of the polarizing film did not break. The characteristics of the obtained polarizing film are shown in Table 3.

<Comparative Example 1> In the first embodiment, the film obtained by the film formation was obtained in the same manner as in Example 1 except that the film was stretched in the width direction (TD direction) using the stretching machine. A vinyl alcohol film (width 2 m, thickness 60 μm, length 2 km). The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. The characteristics of the obtained polarizing film are shown in Table 3.

<Comparative Example 2> In the same manner as in Example 3, the film obtained by the film formation was obtained in the same manner as in Example 3 except that the film obtained by the film formation was not extended in the width direction (TD direction). A vinyl alcohol film (width 2 m, thickness 20 μm, length 2 km). The properties of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Further, this polyvinyl alcohol-based film was used in the same manner as in Example 1 to obtain a polarizing film and a polarizing plate. The characteristics of the obtained polarizing film are shown in Table 3.

[Table 1]

[Table 2]

[table 3]

From the results of the above examples and comparative examples, it is understood that the ratio of the degree of swelling X (%) obtained in the width direction (TD direction) to the degree of swelling Y (%) in the direction of travel (MD direction) satisfies the aforementioned condition (1). And (2) the polarizing films of Examples 1 to 3 of the polyvinyl alcohol-based film of the range specified, which have a high degree of polarization and no color unevenness. On the other hand, the ratio of the swelling degree X (%) derived from the width direction (TD direction) to the swelling degree Y (%) of the traveling direction (MD direction) is within the range specified by the above conditions (1) and (2). In the polarizing films of Comparative Examples 1 and 2 of the outer polyvinyl alcohol-based film, the degree of polarization was poor and color unevenness was also observed.

It can also be seen that the intersection angle θ (°) obtained from the in-plane phase difference (Rxy) and the alignment axis (late phase axis) and the width direction (TD direction) satisfies the conditions specified in the above conditions (4) and (5). The polarizing films of Examples 1 to 3 of the polyvinyl alcohol-based film of the range have a high degree of polarization and no color unevenness. On the other hand, the intersection angle θ (°) derived from the in-plane phase difference (Rxy) and the alignment axis (late phase axis) and the width direction (TD direction) is specified by the above conditions (4) and (5). In the polarizing films of Comparative Examples 1 and 2 of the polyvinyl alcohol-based film outside the range, the degree of polarization was poor and color unevenness was also observed.

The specific embodiments of the present invention have been disclosed in the above embodiments, but the above embodiments are merely illustrative and not limiting. Various changes that are obvious to those of ordinary skill in the art are intended to be included within the scope of the present invention. [Industrial use]

The polarizing film and the polarizing plate of the polyvinyl alcohol film of the invention have excellent polarizing performance, and are suitable for use in a portable information terminal, a personal computer, a television, a projector, a signboard, a desktop computer, and an electronic device. Liquid crystal display devices such as clocks, word processors, electronic papers, game machines, video recorders, cameras, photo albums, thermometers, stereos, automobiles, and mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, wearable displays Anti-reflection layer, optical communication equipment, medical equipment, building materials, toys, etc. for display elements (CRT, LCD, organic EL, electronic paper, etc.).

no

Claims (15)

A polyvinyl alcohol-based film for producing a polarizing film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, characterized in that the polyvinyl alcohol-based film is immersed in water at 30 ° C for 15 minutes, and has a width direction. That is, the degree of swelling X (%) in the TD direction and the degree of swelling Y (%) in the length direction, that is, in the MD direction, satisfy the following conditions (1) and (2): (1) 110 ≦ Y ≦ 140; (2) 1.01≦Y/X≦1.2. The polyvinyl alcohol-based film for producing a polarizing film according to the first aspect of the invention, wherein the polyvinyl alcohol-based film is immersed in water at 30 ° C for 15 minutes, and the degree of swelling Z (%) in the thickness direction satisfies the following Condition (3): (3) 140≦Z≦170. The polyvinyl alcohol-based film for producing a polarizing film according to the first or second aspect of the patent application has an offset ΔX (%) in the width direction, that is, a swelling degree X (%) in the TD direction, and an MD direction in the longitudinal direction. The offset ΔY (%) of the degree of swelling Y (%) and the offset ΔZ (%) of the degree of swelling Z (%) in the thickness direction are both within 5%. The polyvinyl alcohol-based film for producing a polarizing film according to the first or second aspect of the patent application satisfies the following conditions (4) and (5): (4) In-plane retardation Rxy (nm): 100 to 200 nm (5) The alignment axis, that is, the intersection angle θ (°) of the retardation axis and the width direction, that is, the TD direction is 20° or less; the in-plane phase difference Rxy (nm) is in the polyvinyl alcohol film. The width direction, that is, the refractive index in the TD direction is nx, the longitudinal direction, that is, the refractive index in the MD direction is ny, and the thickness is d (nm), the value calculated by the following formula (A): (A) Rxy (nm) )=|nx-ny|×d(nm). The polyvinyl alcohol-based film for producing a polarizing film according to the fourth aspect of the invention is offset by ΔRxy (nm) in the width direction, that is, the in-plane retardation Rxy (nm) in the TD direction is 10 nm or less. The polyvinyl alcohol-based film for producing a polarizing film according to the fourth aspect of the patent application has an offset Δθ (°) of a crossing angle θ (°) of 10° or less. The polyvinyl alcohol-based film for producing a polarizing film according to the first or second aspect of the patent application has a thickness of 5 to 30 μm. A polarizing film characterized by using a polyvinyl alcohol-based film for producing a polarizing film according to any one of claims 1 to 7. A polarizing plate comprising: a polarizing film according to item 8 of the patent application; and a protective film disposed on at least one side of the polarizing film. A method for producing a polyvinyl alcohol-based film for producing a polarizing film, wherein an aqueous solution of a polyvinyl alcohol-based resin is formed by a continuous casting method, and after being peeled off from a casting mold, it is conveyed in a direction of travel, that is, in an MD direction. The polyvinyl alcohol-based film is continuously dried and stretched in the width direction, that is, in the TD direction, and is characterized in that the polyvinyl alcohol film is immersed in water at 30 ° C for 15 minutes, and the width direction is TD. The degree of swelling X (%) in the direction and the direction of travel, that is, the degree of swelling Y (%) in the MD direction, satisfy the following conditions (1) and (2): (1) 110 ≦ Y ≦ 140; (2) 1.01 ≦ Y /X≦1.2. A method for producing a polyvinyl alcohol-based film for producing a polarizing film according to claim 10, which is stretched at a stretching ratio of 1.05 to 1.5 times in the width direction, that is, in the TD direction. The method for producing a polyvinyl alcohol-based film for producing a polarizing film according to Patent Application No. 10 or 11 is carried out at 50 to 150 ° C in the width direction, that is, in the TD direction. The method for producing a polyvinyl alcohol-based film for producing a polarizing film according to claim 10 or 11, wherein the film has a water content of 0.5 to 15% by weight in the width direction, that is, before the stretching in the TD direction. A method for producing a polyvinyl alcohol-based film for producing a polarizing film according to claim 10 or 11, which temporarily extends more than 1.3 times in the width direction, that is, in the TD direction, and then in the final width direction, that is, the TD direction. The stretch ratio is 1.05 to 1.5 times, which causes the size to shrink. A method for producing a polyvinyl alcohol-based film for producing a polarizing film according to Patent Application No. 10 or 11, wherein the dimensional change rate of the film in the MD direction is before and after the extension in the width direction, that is, in the TD direction. 0.8~1.0.